This invention relates to an arrangement for electronically processing photographs and more particularly is directed to an analog system adapted for aiding doctors in reading human X-ray photographs, or law enforcement officers in looking for hidden explosives in luggage, etc.
When taking human X-rays, the dosage must necessarily be very limited so that neither the patients nor the person involved in taking the X-ray are exposed to too much radiation. Because of the limited dosage of radiation, or, more generally, when looking for low contrast objects in X-ray pictures, as, for example, resulting from plastic explosives, soft tissue abnormalities, etc., the X-ray picture tends to have deviations or islands of grains which create background noise when the photograph is scanned and displayed by a TV picture system which introduces additional noise. In the past, this problem has been attacked by passing the electronic signal picked up by a TV camera through a filter of averaging device. However, noise remains a limiting factor and particularly interferes with a doctor's ability to detect small changes in a relatively large body organ such as might be the case when the doctor is trying to read an X-ray photograph to determine if a patient has an inflamed appendix; or in equivalent cases in a more general context. There are, of course, complex computerized techniques for processing X-ray photographs but these require complex and expensive equipment beyond the budget of most medical facilities or other users and require a technical expertise in a completely different field well beyond the skill of even the most able medical doctor, or other users who may have a need for such devices.
Most if not all of the approaches to improvement of the readability of X-ray pictures other than perhaps certain computer techniques rely on edge enhancement in one form or another. Such approaches do not overcome or attempt to overcome the basic problem in X-ray picture interpretation, the limitation on information recognition resulting from noise. There is no attempt in such devices to literally dig the available information out of the noise. Edge enhancement does not accomplish this and in fact only enhances what is already visible and thus has found little acceptance in the 20 years since issuance of the Kovasznay U.S. Pat. Nos. 2,900,442 and 2,903,507.
Information theory as developed by Wiener and others defines the interplay between the limitation of recognition of density differences and size of objects detectable but no approach known to the inventor has been made that applies the general knowledge in this field to viable methods of improving techniques of reading X-ray pictures.
The present invention is directed to an electrical system which is of relatively simplified and inexpensive construction and which permits as a limiting case all information available in an X-ray film (or the like) to be extracted.
The basic components of the system consist of a TV camera for reading the X-ray photograph, a low pass filter for filtering out noise, a window amplifier for electronically processing or enhancing the display and a TV monitor or display tube for presenting either a normal or processed display of the X-ray photograph to the doctor or X-ray technician.
The present invention recognizes that in order to detect relatively small changes in signal which in one example are indicative of changes in soft tissue, the signal-to-noise ratio of the information must be greatly improved so that contrast (represented by signal amplitude differences) can be expanded without destroying the ability to detect meaningful signals. The system has certain constraints: (1) frame rate must not introduce flicker, typically not less than 60 frames/sec or 30 frames/sec with interlaced scans, (2) the beam size should be small enough to detect the smallest desired object but no smaller since in all films (X-ray and others) as well as the camera viewing surfaces, grain produces large amounts of noise and the smaller the beam the more the noise; (3) the scan rate (and therefore number of lines per frame) should be kept low to maintain the information signals at as low a frequency as possible keeping in mind that grain and conventional video noise is concentrated at higher frequencies, and (4) in order to detect all desired detail, all parts (i.e. areas) of the picture or other object or view to be investigated must be interrogated. Thus, unlike conventional T.V., scan lines preferably should abut one another so that no detail is lost.
The present system includes a window amplifier or slice amplifier with a knob by means of which the viewer may vary the contrast intensity of the display on a TV monitor from a normal display to a maximum contrast intensity over a predetermined but variable range of intensities. The purpose is to give the user maximum control over the diagnosis of such things as an inflamed appendix, lung lesions and the like whereby if desired, he may switch back and forth between normal and various intensity displays until he is satisfied with his diagnosis of the X-ray photograph under consideration. Density variations are not great when viewing soft tissues or the like and the object to be viewed may be of the order of one centimeter in diameter. It is necessary therefore to enhance contrast, a process which per se increases noise effects, an effect which cannot be tolerated. In the present invention a large proportion of the noise effect is eliminated prior to increasing contrast thereby reducing total noise while enhancing desired image contrast.
Photograph light intensity differences are increased by passing the output of a low pass filter connected to a TV camera through a window or slice amplifier. An entire photograph is scanned at 60 Hz either in a conventional manner or alternately by first a horizontal sweep, then a vertical sweep. When employing the criss-cross scan the picture is illuminated by stroboscopic light flashes after the completion of both the horizontal and the vertical scan. The electrical output passes through a low pass filter to give long-term averaging (filtering) in both vertical and horizontal directions. Picture tube and TV camera dot size can be increased (both for interlace and no interlace) and sweep speed reduced (also number of lines reduced) as compared with normal high resolution TV picture systems.
It is therefore one object of the present invention to provide an improved picture processor or visibility expander.
Another object of the present invention is to provide a relatively simplified analog type electronic visibility expander.
Another object of the present invention is to provide a visibility expander particularly adapted for use by physicians and/or medical technicians in reading human X-ray photographs.
Another object of the present invention is to provide a simplified and inexpensive visibility expander of general utility for use by the medical profession, law enforcement agencies and the like.
Another object of the present invention is to provide a relatively simplified and inexpensive circuit device which may be used as a human element diagnostic tool at almost all medical facilities.
Another object of the present invention is to provide a relatively simplified and inexpensive device for detecting light intensity differences in all types of X-ray photographs and for other transparencies or pictures.